The purpose of this research is to determine the effectiveness of two medications, tricyclic antidepressants (TCA) and opioids, compared to a placebo in the treatment of Post-Herpetic Neuralgia. The specific aims are to compare the effects of opioids and TCA against placebo on pain, altered skin sensitivity, and affective and cognitive function. In addition, the study will determine if the therapy with opioids or TCA affects cognitive function that may limit their usefulness in the treatment of PHN. We have studied the relationships between ongoing pain, alterations in thermal sensibility, and allodynia to mechanical and thermal stimuli of patients with PHN to determine the role of peripheral and/or central mechanisms in PHN. Ongoing pain ratings were obtained using a verbal score (0-10). Sensory tests were performed within the affected site, and the corresponding, contralateral, normal site. The area of mechanical allodynia was mapped with a cotton swab and pain evoked by mechanical stimuli (soft hair brush, brass probe, von Frey hairs) was rated on a verbal scale of 0-10. Thermal thresholds to warm, cold, heat pain, and cold pain were determined using a Peltier device and a modified Marstock technique. Measures of cognitive function included the Digit symbol test, Digit Span, a digit cancellation test, the grooved pegboard, and a measure of verbal learning.